Amplifier circuits



Feb. 7, 1928. 1,658,346

R. C. MATH ES AMPLIFIER CIRCUITS Filed Nov. 7, 1919 @Wny Patented Feb. 7, 1928.

1,658,346 PATENT OFFICE.

ROBERT C. MATHES, 01's NEW'YORK, N. Y., ASSIGNOB TO WESTERN ELETBIC H PANY, INCOBPORTEB, OF NEW YORK, N. Y., A CORPORATION OF NEW YORX.

AMPLIFIER CIRCUITS.

Application flled November 7, 1919. Serial No. 836,352.

' This invention relates to amplifier circuits and has for an object the provision of meth- 06.3 and means for increasmg the amount of amplification that may be secured from an amplifier, articularly of the'aud1on type.

' As is We l known in the art, a vacuum tube may be employed for amplifyin51 currents since any im ulse impressedon e control electrode of tne tube Will appear in amphfied e form in the output circuit 0 the tube. This invention comprises associating the output circuit of the tube with the imput circuit of the tube in such a manner that a portion of the amplified energy in the output circuit Will be fed back into the input circuit to be re-amplified, thereby increasing enormously the degree of am lification that may be obtained from a .tu c of a given type. One way this eed-back of energy may be accomo plished is described and claimed in my copending application, Serial No. 336,351, filed November 7 1919.. As described therein, the energyfeed-back is accomplished by a transformer, one winding of which is in the 5 output circuit of the tube, the other winding of which is located in the tubes input circuit. It has been found that it is necessary to limit the amount of energy that is transferred back to the input circuit in order to prevent 0 the tube from singing. One way the amount of energy fed back may be limited is to place a resistance in shunt to one of the transfromer Windings. It is frequently desirable that the increased amplification obtained from 5 the feed-back be as uniform as possible over a wide' frequency range, and this also is accomplished by placing the resistance in shunt to the transformer.

It has been found, however, that the degree of amplification secured by the above described arrangement still depends somewhat upon the frequency of the impulses to be amplified. This amplification inequality is due chiefiy to the fact that the output circuit of' an amplifier usually includes load apparatus such as receivers, coils and the like, Which have impedance characteristics which vary with the frequency, so that With such load apparatus in the output circuit, it is difficult to control the amplification to a uniform degree over a wide frequency range.

In accordance With this invention, the action of such load apparatus upon the operation of the feedback circuit is substantially eliminated by providing an amplifier having an output circuit of two branches, in One accomplished, the other branch being assowhich vary with the frequency. In the referred form of this invention, this branc ed output circuit is secured by employin "a vacuum tube which has two anodes and y connecting the feed-back transformer in circuit with one of said anodes and by connecting the Outgoing load line or transformer in circuit with the other of the anodes, thereby making the energy feed-back substantially independent of the frequency of the impulses to be amplified,

This invention Will be better understood by reference to the following 'detailed description taken in connection with the ac companying drawings in which Fig. 1 shows this invention in connection with a vacuum tube amplifier having two anodes; Fig. 2 is a modification of Fig. 1.

Referring to Fig. 1, 4 is a vacuum tube having a cathode 5, two anodes 6 and 7 and a control electrode consisting of two grids 8 and 9. Heating current for cathode 5 is supplied by source of voltage 12. The input circuit of the tube may be traced from grids 8 or 9, secondary of input transformer l4, winding 15 of transformer 16 t0 cathode 5. One branoh of the output circuit of the tube may be traced from anode 6, primary winding of the outgoing load circuit transformer 18, source of voltage 19 to cathode 5. The second branch of the output circuit ma be traced from anode 7, winding 21 of the cedback transformer 16, source of voltage 19 t0 cathode 5. With such an arrangement, the signals to be amplified which may come from source 23 Willbe impressed on grids 8 and 9 by' transformer 14, thereby producing impulses in amplified form in both branches of the output circuit of the tube. Since winding 21 of transformer 16 is in the out ut circuit*of the tube and winding 15 o 'transformer 16 is in the input circuit of the tube, a portion of the amplified ener in that part of the output circuit Whic contains winding 21 Will be fed back. to the inputcircuit of the tube through transformer 16.

This amplified energy will thenbe impressed on grids 8 and 9 so that the signaling impulse be amplified again by tube 4. In order that the amount of energ; fed back to the :ciated vvith outgoing transformrs, receivers, or the hke load apparatus, the impedances of to sing. The amplified impulses in that part of the output circuit in the primary Winding of transformer 18 Will be impressed upon the outgoing line 27 WhlCh maymclude a receiver 28 or 1ike load device. Owing to the fact that the outgoing line or load is associated with that part .of the output circuit of tube 4 which does not include the feedback transformer, the amount of amplification derived from tube 4 will be substantially independent of the impedance characteristics of the line 27 or transformer 18 or load device 28.

In order to secure a wider frequency range of increased amplification, it is possible to feed back a portion of the energy in both branches of the output circuit instead of only one branch as shown in Fig. 1. However, in such a case, it is still preferable that most of the energy fed back should be fed back by means of a transformer which is located in that branch of the output circuit which is not associated with the load apparatus.

An arrangement of this kind is shown in Fig. 2, Where tube 30, similar to tube 4, has

' a branched output circuit. 'One branch consists of an anode 31, primary winding of outgoing or load transformer 32, primary winding of feed-back transformer 33, source of voltage 34 to' cathode 35. The other branch of the output circuit includes an anode 37, primary winding of feed-back transformer 38, source of voltage 34 and cathode 35. The secondary windingsbf transformers 33 and 38 are shunted by resistances 40 and 41 in order to prevent the tube from singing as above described. The second feed-back transformer 33 sho'uld preferably have its greatest feedback efiiciency for frequencies other than those where the eficiency of the first feed-back transformer is the greatest, thereby serving t0 broaden the frequency range 'of nearly uniform amplification. The frequencies at which each transformer has its greatest efficiency depend upon several factors, primarily upon the relative mutual impedance between the windings. Since the mutual impedance between the windings of a transformer is proportional to the product of the number of turns of the primary winding times the number of turns of the secondary winding, it follows that the desired tesult may be obtained by making this product for transformer 33 different from the product for transformer 38. It is pref erable, however, that most of the energy fed back to the input circuit of tube 30 should be through the transformer 38, since the energy fed back through transformer 33 Will depend somewhat upon the frequency of the impulses to be amplified.

It is to be understood'thit this invention is not limited to the particular forms described above, but that it may be variously modified without departing in anywise from the spirit of this invention, as defined in the appendecl claims.

What is claimed is:

1.,A repeater device comprising a vacuum tube having a plurality of space current paths, an input circuit and a plurality of output circuits for said vacuum tube, said output circuits utilizing different space current paths in said vacuum tube, means to feed back energy from one of said output circuits to the input circuit and means to supply a load circuit from another of said output circuits.

2. A repeater device comprising a vacuum tube having a cathode, a control element, and a plurality of anodes, means to establish an electron stream between said cathode and each of said anodes, means to feed back energy of current from one of said electron streams to the control element and means to supply a load circuit from the other of said streams.

3. A repeater device comprising a vacuum tube having a cathode, a control clament, and a plurality of anodes, means to establish an electron stream between said cathode and each of said anodes, means for connecting the circuit of one of said streams to the control element and means to connect the circuit of the other stream to a load circuit.

4. The combination of a controlling circuit comprising a control electrode, a controlled circuit including a stream of electrons between a pair of electrodes, a second controlled circuithaving an electron stream between one of said pair of electrodes and a third electrode, means to couple said two firstmentioned circuits, and means to suppl' a load circuit from said second controlled circuit.

5. In an electric system, a vacuum tube having a cathode, a control electrode and a plurality of anodes, means for supplying to said control electrode impulses to be amplified, outgoing terminals for said tube, an electric circuit between one of said anodes and said cathode comprisingsaid outgoing terminals, and an electric circuit between said cathode and another of said anodes comprising means for feeding back to said control electrode a portion of the amplified energy in said second electric circuit.

6. In an electric system, a vacuum tube having a cathode, a control electxode and a plurality of anodes, means for supplying to said control electrode impulses to be amplified, outgoing terminals for said amplifier,

21 transformer having a plurality of windings, an electric circuit between said cathode and one of said anodes comprising said outgoing terminals, an electric circuit between sa id cathode and another of said anodes comprising a winding of said transformer, an electric circuit between said cathode and control electrode comprising a second wind-.

ing of said transformer, and means comprismg a resistance shunted around one of said windings to render the energy fed back having an input circuit and a branched output circuit, means for feeding back to said input circuit a portion of the ener' in sa1d output circuit, said means being ocated in one branch of said output circuit, and an outgoing lino associated with anotherbr&nch of said out ut circuit, said branches compri)sing di erent electron streams in said tu c.

8. In an electric system, 21, vacuum tube having an input circuit and a branched output circuit, 8. transformer havin a winding in said output circuitand a win ing in said input circuit, a resistance in shunt to one of sa1d windings, and outgoing terminals associated with another branch ofsaid output circuit, said branches comprising diferent electron streamsin said tube.

In witness whereof, I hereunto subscribe my name this 3rd day of November, A. D.,

ROBERT c. MATHES, 

